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#1068919 - 12/15/20 11:12 AM tach accuracy  
Joined: Jun 2001
Posts: 1,486
markg Online content
15+ Year
markg  Online Content
15+ Year

Joined: Jun 2001
Posts: 1,486
how accurate ia my factory 86 tach?
i put a 383 in one of my cars and its got a victor jr open plenum intake thats good for 3500 to 8000 rpm.
i never go way up there in my driving.once broken in i got to romp on it a bit.
the car is still pulling hard but the tach is absolutely pinned at 6000.
thats kinda scary for me.
it also seems to be showing a lot higher idle rpm that i think it should be comparted to my jeep with an aftermarket tach and a bigblock chevy.
the jeep will idle at 500 if i want it to but my monte would never go down to 500 wo stalling.
i have a new manifold coming thats a lower rpm range (7501 air gap)
thats the one most recommended and its got a range of 1500 to 6500 rpm

86 ss 86 cl,330hp GM vortec cratemotor-700-r trans worked,ford 9.5 inch rear with 3-50s,custom 3 inch exhaust with flowmasters.
#1068921 - 12/15/20 03:22 PM Re: tach accuracy [Re: markg]  
Joined: May 2004
Posts: 983
BladeOfAnduril27 Online content
15+ Year
BladeOfAnduril27  Online Content
15+ Year

Joined: May 2004
Posts: 983
Doylestown, PA
They lose accuracy with age and read high. There is a write-up in the DIY board on how to fix:

~ Matt H.

1988 Monte Carlo SS w/ T-tops, White with gray int, 350, Summit cam, World Torquer S/R heads, Holley St. Dominator intake, Edelbrock 600cfm carb, Champion 3-row alum radiator, ramchargers, 200-r4 with CK Shift Kit, billet servo, 2200 stall, Afterburner headers, Pypes 2.5" with x-pipe, Violator mufflers (stock exit), S10 front brake swap.

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